Fixed bug 'TypeError: event.dataTransfer is undefined'

The bug occurs when **jQuery** is used with **Angular**. It's because of:

>"If jQuery is available, angular.element is an alias for the jQuery function. If jQuery is not available, angular.element delegates to Angular's built-in subset of jQuery, called "jQuery lite" or "jqLite." (https://docs.angularjs.org/api/ng/function/angular.element) 

and because of jQuery event object does not have a **dataTransfer** property. (http://api.jquery.com/category/events/event-object/)